1. Field of Invention
This invention relates to a technique for monitoring one or more process variables of media flowing in a pipe; and more particularly relates to a technique for monitoring one or more process variables of media flowing in a pipe having a liner therein.
2. Description of Related Art
In processes where erosion of process pipes occur at high rates (i.e. Oil Sands slurry transport), lined piping has shown improved resistance to wear, as shown in FIG. 1.
There are known techniques for measuring flow rate and/or wall thickness to predict when a pipe should be replaced. For example, FIG. 2 shows one such known technique where a piezo polymer may be arranged on a pipe wall. However, in operation when a voltage signal causes a piezo polymer pulse, it will reflect off a rubber intermediate layer, but there is little or no energy reflected back off the liner, which could be used to measure the flow rate or pipe wall thickness, among other process variables, using the known technique.
Because of this, the benefit of lined pipe is offset by the difficulty in measuring the pipe wall thickness to predict when the pipe should be replaced, despite the improved wear rate. Failure to replace the pipe at the appropriate time can lead to ruptures and process down time. Standard wall thickness measurement techniques are inadequate due to the construction of the lined pipe. The ultrasonic pulse does not couple well to the inner lining because of the acoustic impedance mismatch. Many lined pipe design further complicate the problem by using a soft compliant layer between the outer metal and the inner core of the pipe.
For all these reasons, there is a need in the industry for a way for measuring flow rate and/or wall thickness in a lined pipe in order to predict when a pipe should be replaced.